A cylindrical glass container $($diameter $45$cm$)$ filled with liquid aniline is stored

in a large room. The ambient air $(1$ atm$)$ is initially aniline$-$free and the room temperature is constant at

$20$ degree C$.$ At t$=0,$ the lid of the container is removed and the aniline evaporates slowly. Saturation

vapor pressure of aniline is $0\mathrm{.}5$ kPa. Molecular weight of aniline is $93$ g$/$mol$.$ The diffusion coefficient $($D$)$

of aniline in air is $0\mathrm{.}082$ cm$2/$s$.$

a$)$ Calculate the concentration of aniline in the air at $15$ cm above the surface of the container after $4$ min.

b$)$ How much mass of aniline will have evaporated after $4$ min?